This invention relates to compositions useful for curing polyurethane prepolymers, to a process for preparing such curing compositions, and to curable compositions made by mixing such curing compositions with isocyanato-terminated prepolymers.
It is known that compositions useful in curing isocyanato-terminated polyurethane prepolymers can be made by dispersing particles of a complex of 4,4'-methylenedianiline (MDA) with a salt in an inert organic liquid. However, such prior art compositions have the drawback that their mixtures with polyurethane prepolymers have poor shelf life, as indicated by their tendency to undergo an undue increase in viscosity during storage. There is a need in the art for a curing composition which forms mixtures with prepolymers having good shelf life at room temperature and slightly above, and having the ability to cure rapidly at an elevated temperature to form well-cured polyurethane products.
U.S. Pat. No. 4,075,150 to Hoeschele addresses the same problem. The drawback of that invention, however, is poor hydrolytic stability of polyurethanes prepared by that process.